U.S. Pat. No. 8,682,001, by Annunziato et al., incorporated here by reference, describes an in-ear active noise reduction (ANR) headset that includes two microphones in each earbud, one inside the acoustic system for providing feedback-based ANR, and one outside the acoustic system for providing feed-forward-based ANR. In a commercial product embodying that patent application, the Bose® QC® 20 Acoustic Noise Cancelling® headphones, a fifth microphone was provided, in the cable joint housing of the headphone cable, for picking up the user's voice for use in communications applications. Other in-ear headphone products tend to also include communications microphones somewhere in the headphone cable, rather than in the earbud, as do many on-ear and around-ear headphones.
Detecting the voice of a user of headphones is useful for at least two reasons. First, it provides near-end audio for transmitting to a communication partner. Second, headphones, and in particular ANR headphones, tend to distort how the user hears his own voice when speaking, which we refer to as self-voice. Playing back the user's own voice within the headphones, which we refer to as side-tone audio, allows the user to hear his voice, and properly modulate it for conversation either with an electronic communication partner or face-to-face. Providing an accurate side-tone requires good voice detection.